In a mobile communications system, an authentication algorithm is developed to authenticate a user's identity so as to prevent fraudulent use of services. Communications services such as banking services, credit card services, automatic teller machine services and general information services require that a user be accurately identified for the purpose of security, proper billing and avoidance of fraud.
Using the authentication algorithm, an authentication key is created first by a communications agency which deals with services such as a terminal set up and a number change requested by mobile subscribers; and then an authentication procedure is performed with the authentication key created. Normally, the authentication key is created immediately after giving to subscribers of new mobile stations telephone numbers, whereas the authentication procedure is performed whenever the user employs a service. The authentication key is conventionally obtained by an authentication key generation scheme which employs several variable parameters for data security and reliability in the communications agency.
However, the conventional authentication key generation scheme has a shortcoming in that it does not allow the authentication key by any other to be generated except the communications agency, thereby inconveniencing the mobile station's subscribers.